1. Field
Embodiments relate to an organic light emitting diode (OLED) display and a driving method thereof.
2. Description of the Related Art
In a display device, a plurality of pixels are disposed in a matrix form on a substrate so as to be used as a display area, scan lines and data lines are connected to pixels, and data signals are selectively applied to the pixels to display an image.
Currently, display devices are divided into a passive matrix type of light emitting display device and an active matrix type of light emitting display device depending on how pixels are driven. Among them, the active matrix type of light emitting display device, in which unit pixels are selectively turned on, is becoming mainstream in terms of resolution, contrast, and operation speed.
Such a display device is used as a display device for mobile information terminals such as a personal computer, a mobile phone, a personal digital assistant (PDA), and the like, or as a monitor of various information devices, and a liquid crystal display (LCD) using a liquid crystal panel, an organic light emitting diode (OLED) display device using an organic light emitting element, a plasma display panel (PDP), and the like, are widely known as the display device. Among them, an OLED display device having excellent luminous efficiency, excellent luminance, a wide viewing angle, and a fast response speed, has received much attention.
In the case of the OLED display device, gray levels are represented by current flowing across an OLED and a driving transistor is used to control current supplied to the OLED. Operation regions of the driving transistor are divided into a saturation region and a linear region. In general, a source electrode of the driving transistor is fixed as a certain power source voltage and a data voltage input to a gate electrode of the driving transistor is changed according to a gray level.
Thus, in order for the driving transistor to control current supplied to the OLED according to a data voltage, the driving transistor must operate in the saturation region. If the driving transistor operates in the linear region, current flowing across the driving transistor would be changed according to a drain-source voltage, so even when the same data voltage is applied, a different current may be supplied to the OLED according to the driving transistor. In order for the driving transistor to operate in the saturation region, the drain-source voltage of the driving transistor must have a higher level than that of a certain saturation voltage.
Meanwhile, the driving voltage of the OLED changes according to the temperature of the display device or due to degradation of the OLED resulting from prolonged use of the display device with the passage of time. As the use time of the display device is lengthened, the driving voltage needs to be increased to apply the same current due to gradual degradation of the OLED itself. In addition, the driving voltage varies according to a change in temperature such as a low temperature, room temperature, and a high temperature.
The above information disclosed in this Background section is only for enhancement of understanding and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.